The present invention relates generally to control systems and in particular to those which may be utilized to control a certain condition in an enclosed space.
In the past, many different types of control systems were provided for regulating or controlling a certain condition, such as temperature for instance, in an enclosed space, such as an oven or the like. Some of these past control systems were, for the most part generally mechanical in nature having at least some of the disadvantageous or undesirable features normally attendent to mechanical devices. Others of these past control systems were, for the most part, solid state electronic devices.
Due to the vertically instantaneous reaction of control systems of the solid state type to condition changes, one of two general approaches was employed in prior art circuitry to limit cycling of the system components so as to provide a stable operating mode for the control system. For instance, one approach was to enable a means for changing a condition, such as temperature for instance, in an enclosed space, during only a portion of each cycle of alternating current supplied thereto and to vary the proportion of each cycle during which the condition changing means was enabled in response to a sensed temperature in the environmental space. The other of the two approaches employed in prior art circuitry to prevent undue cycling of the system utilizes some types of additional circuitry for causing a turn-on temperature to be different than a turn-off temperature thereby to insure that means for changing the condition in the enclosed space is energized for a reasonable length of time when such energization is indicated by the control system. In many prior art control systems, this latter scheme was implemented by providing a capacitor for creating a differential amplifier and discharging the capacitor each time a control element, such as a silicone controlled rectifier, was rendered conductive.